Meanwhile, experts tell CBS News correspondent Sheila MacVicar that the bombs the suspects were allegedly trying to make may not have worked.
Sources close to the investigation tell MacVicar they believe the suspects were trying to make acetone peroxide. But this chemical has a strong smell and is very unstable — sensitive to even small rises in temperature. Would-be bombers may not have been able to keep the solution cool enough, experts say.
In London Tuesday, police cars with lights flashing and sirens blaring cleared the way for vans carrying the suspects to the City of Westminster Magistrates Court in central London. Journalists lined the streets behind barricades erected to keep roads clear.
Tanvir Hussain, 25, Ahmed Ali, 25, Umar Islam, 28, Arafat Khan, 25, Assad Ali Sarwar, 26, Adam Khatib, 19, Ibrahim Savant, 25 and Waheed Zaman, 22, all were ordered held until a second court appearance on Sept. 4.
Hussain's lawyer, Mohammed Zeb, told the judge: "All allegations are denied."
A dozen family members and a swarm of journalists squeezed into the courtroom. Each suspect was accompanied by a guard and stood in the dock protected by heavy glass. As they were led away, Khan and Islam smiled at people in the public gallery.
Three others charged with lesser offenses were also ordered held until a court appearance next week, including a 17-year-old male charged with possessing material which could be used to prepare a terrorist act.
The other two — Cossar Ali, 24, Ahmed Ali's wife, and Mehran Hussein, 24, — were charged with failing to disclose information that could help prevent a terrorist act.
The Crown Prosecution Service said the suspects probably would go on trial sometime in 2007. Because of the number of suspects, proceedings may be split into two or more trials, which could last many months.
Another person was released Monday without charge, while 11 still in custody have not yet been charged. Investigators have until Wednesday to decide if the suspects — whose names have not been released by police — will be charged, released or if police will ask a judge to grant them more time to investigate.
"Their position is being assessed on a regular basis with a view to considering the need to keep them in detention," said Susan Hemming, who heads the Crown Prosecution Service's Counter-Terrorism Division. "The evidential picture is continuously developing."
The evidence was being examined in minute detail, Peter Clarke, the head of the Metropolitan Police's anti-terrorism unit, told reporters after the Crown Prosecution Service announced the charges Monday.
"The meticulous investigation of all this material will take many months. All the data will be analyzed. There will be thousands of forensic examinations and comparisons," he said. "The scale is immense, inquiries will span the globe."
British officials also confirmed for the first time that the plot involved the manufacture of explosives, which would then be assembled and detonated on board the airliners.
"There are chemicals, including hydrogen peroxide, electrical components, documents and other items," Clarke said. "We have also found a number of video recordings — these are sometimes referred to as martyrdom videos. This has all given us a clearer picture of the alleged plot."
More than 8,000 data-storage devices such as compact discs, DVDs and memory sticks, were found. Maps of Afghanistan, suicide notes from willing terrorists and books on explosives also were seized, officials said.
Investigators did not say whether they believe suspects are linked to al Qaeda.
Pakistani officials have linked people arrested in that country in the alleged airline conspiracy to al Qaeda militants in Pakistan and Afghanistan. Authorities in Pakistan are still interrogating Rashid Rauf, a Briton of Pakistani descent, over his alleged key role in the plot, officials said. Rauf's brother, Tayib, was among those not charged but still in custody in Britain.